This invention relates to hydraulic apparatus for supplying fluid to implement and steering circuits used for vehicles such as articulated shovel loaders.
Generally, a hydraulic apparatus of an articulated shovel loader comprises three pumps, including one change-over pump, driven by a propulsion engine of a vehicle and a flow dividing valve delivering fluid, usually oil, from the change-over pump to steering and implement circuits in accordance with revolutions of the engine. With the hydraulic apparatus thus constructed, when the engine is driven at a low or neutral speed, the change-over pump is always communicated with the steering circuit through the flow dividing valve, so that even in a time of low speed steering operation which can be performed with a small amount of oil, since the oil from the change-over pump is added to the oil from a pump for operating the steering circuit, a considerably large amount of oil which is utilized for a high speed steering operation flows into the steering circuit. In addition, the flow of such large amount of oil increases pressures of the steering and change-over pumps.
Thus, a potential energy of a large amount of excess oil to be discharged into a tank is converted into heat without effectively acting to the steering circuit.